I've seen well balanced planes fly and land without power ( think free flight and failsafe for instances, but others as well) but if the battery falls out (and it wasn'tperfectly positioned on the CoG before falling out )a crash is inevidable. I check my planes every time I fly just like I always fill the tank). I had a Voltwatch on my first trainer, nothing against them, just more weight, more wire connections to come loose.
Mike